Drug interactions
Cyclobenzaprine + Promethazine
Severity: Moderate
Cyclobenzaprine and Promethazine: moderate interaction.
Last updated
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Both drugs are sedating and strongly anticholinergic, so combined use increases drowsiness, dry mouth, urinary retention, constipation and confusion. Cyclobenzaprine is structurally related to tricyclic antidepressants, and combining it with phenothiazines may add to QT and serotonergic concerns.
What this interaction means in plain words
Cyclobenzaprine and Promethazine can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken.
Cyclobenzaprine belongs to Musculoskeletal; Promethazine belongs to Respiratory.
Why it happens
Additive CNS depression and muscarinic receptor blockade.
What to do
Use the lowest effective doses and monitor for oversedation and anticholinergic effects, particularly in older adults. Consider an alternative to one of the agents if symptoms develop.
What to ask your pharmacist
- Should I take them at different times of day?
- Does the dose of either medicine need to change?
- Is there anything I should avoid, such as alcohol or certain foods, while on both?
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Other interactions of Promethazine
- Cabergoline + Promethazine Contraindicated
- Dopamine + Promethazine Contraindicated
- Ibutilide + Promethazine Contraindicated
- Pimozide + Promethazine Contraindicated
- Promethazine + Thioridazine Contraindicated
- Alfentanil + Promethazine Major
Other interactions of Cyclobenzaprine
- Cyclobenzaprine + Isocarboxazid Contraindicated
- Cyclobenzaprine + Linezolid Contraindicated
- Cyclobenzaprine + Phenelzine Contraindicated
- Cyclobenzaprine + Safinamide Contraindicated
- Cyclobenzaprine + Selegiline Contraindicated
- Cyclobenzaprine + Selegiline transdermal Contraindicated
Frequently asked questions
Can I take Cyclobenzaprine with Promethazine?
MediHelp rates the interaction as moderate. Cyclobenzaprine and Promethazine can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken. Both drugs are sedating and strongly anticholinergic, so combined use increases drowsiness, dry mouth, urinary retention, constipation and confusion. Cyclobenzaprine is structurally related to tricyclic antidepressants, and combining it with phenothiazines may add to QT and serotonergic concerns.
How serious is the interaction between Cyclobenzaprine and Promethazine?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Use the lowest effective doses and monitor for oversedation and anticholinergic effects, particularly in older adults. Consider an alternative to one of the agents if symptoms develop.
What other medicines interact with Promethazine?
MediHelp also lists interactions of Promethazine with, for example, Cabergoline, Dopamine, Ibutilide. The full list is on the Promethazine page.
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